A mercury porosimeter for investigating capillary phenomena and microdisplacement mechanisms in capillary networks

Abstract

Mercury porosimetry was studied in glass-etched micromodels with the aid of an experimental apparatus that enables the accurate measurement of capillary pressures and mercury saturations, as well as the observation of microdisplacement mechanisms at the pore level. The effect of fluid topology, pore size, and pore body to pore throat aspect ratio during quasi-static imbibition for the air—mercury system is demonstrated in terms of experimentally obtained capillary pressure curves. Imbibition is shown to be determined by the interplay of bond-withdrawal (snap-off in throats) and site-withdrawal (withdrawal from pores) processes. Under conditions of small variability in pore body and pre throat size and for relatively small pore body to pore throat aspect ratio, imbibition phenomena are controlled by the fluid topology in a deterministic manner. That is, withdrawal occurs first from pore throats by the snap-off mechanism and proceeds in pore bodies in a manner that preserves the continuity of the nonwetting phase (nwp). Critical capillary pressures were measured for the withdrawal of mercury from pores and throats under various configurations of capillary interfaces. Theoretical calculations were in qualitative agreement with experimental values. For fully saturated capillary networks, snap-off events in pore throats initiate the withdrawal of mercury. The conjecture that the frontal advance mechanism dominates mercury withdrawal over cluster growth at high initial mercury saturation is not valid for conditions whereby all faces of the pore network are exposed to a mercury sink.